Spark plug incorporating a resistor for providing a low noise level

ABSTRACT

A spark plug incorporating a resistor comprises a ceramic insulator, a metal shell for housing the insulator, an outer electrode connected to the shell and a center electrode opposed to the outer electrode and extended through and sealed in a center bore provided in the insulator, said center electrode being composed of a discharge electrode portion, a conductive glass positioned at one end of the resistor, an auxiliary sealing resistor positioned at the other end of the resistor and a resistor. The conductive glass, the carbonaceous resistor and the auxiliary resistor are placed between the discharge and the terminal electrode portions so as to elongate an effective resistance portion of the resistor.

1111 3,903,453 14 1 Sept. 2, 1975 United States Patent 1191 Nishio SPARK PLUG INCORPORATING A Primary ExaminerR. V. Rolinec RESISTOR FOR PROVIDING A LOW NOISE Assistant Examiner-Darwin R. Hostetter LEVEL Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [75] Inventor: Kanemitsu Nishio, Komaki, Japan NGK Spark Plug C0. Japan Ltd., Nagoya,

[73] Assignee:

. A spark plug incorporating a resistor comprises a ee- [22] Ffled' sept' 1974 ramic insulator, a metal shell for housing the insulator, an outer electrode connected to the shell and a center electrode opposed to the outer electrode and ex- 21 Appl. No.: 509,217

tended through and sealed in a center bore provided in the insulator, said center electrode being composed of a discharge electrode portion, a conductive glass positioned at one end of the resistor, an auxiliary sealing resistor positioned at the other end of the resistor and a resistor. The conductive glass, the carbonaceous resistor and the auxiliary resistor are placed between the discharge and the terminal electrode portions so as References C'ted to elongate an effective resistance portion of the resis- UNITED STATES PATENTS tor.

1864,88 1 12/1958 Counts ct 315/58 x 14 Claims, 1 Drawing Figure SPARK PLUG INCORPORATING A RESISTOR FOR PROVIDING A LOW NOISE LEVEL The present invention relates to a spark plug incorporating a resistor for providing a low noise level.

A spark plug comprising conductive glasses and a resistor sandwiched thereby which are positioned between a center electrode portion and a terminal electrode portion oppositely arranged each other in an insulator consisting of alumina porcelain, can suppress noises or radio frequency interferences generated upon its spark discharge and now has a tendency to be adopted broadly in various combustion engines.

The inventors made various experiments and investigations upon the resistor-incorporated spark plug so as to improve the effect for preventing the noises and as a result, one example in which a noise field intensity of the plug is made small by making the length of the resistor large, at least more than 7 mm, regardless of various values of the resistance and the diameter of the center bore of the insulator used for insertion of the resistor, has been provided (refer to Japanese laid open patent No. 45,725/73).

However, if in order to make the temperature coefiicient at a high temperature small and to have the stable resistance value during spark discharge, the composition of the resistor for use in the spark plug consists of a glass, a ceramic material such as mullite, zircon, alumina, Zirconia and clays as an aggregate, and carbonaceous materials such as glycerin, sugar and polyvinyl alcohol, the composition of the resistor is filled and heat-sealed with the conductive glass between the terminal electrode and discharge electrode portions opposing each other in the center bore of the insulator, and the length of the resultant in the bore is made more than 7 mm, an effective noise preventing effect shall be maintained for a long period of time, but the length of the insulator becomes too long.

Attempts have also been made to use conductive glass consisting of a metal powder, and a glass powder which serves as a sealing agent is omitted, and the resistor is directly provided between the discharge electrode portion and the terminal electrode portion so that the resistor is connected with the discharge electrode and terminal electrode portions and sealed in the spark plug insulator bore. As a result of this it is found that at the contact surfaces of the resistor to the discharge electrode and terminal electrode portions, the carbon in the composition of the resistor is liable to burn upon the spark discharge, so that a whole resistance value of the resistor varies and thus the use of an electrically conducting and sealing means like the conductive glass between the resistor and the electrodes is somehow inevitable.

An object of the present invention is to provide a spark plug incorporating a resistor which is so formed as to eliminate the above described defects.

The present invention is based on the recognition of the fact that the noise field intensity (the smaller, the better) rather corresponds to the length of the resistor and not to the resistance value thereof, so that if the space occupied by, the conductive glass is utilized as a part of resistor, the length of the effective resistance portion will be elongated without undesired elongation of the length of the insulator, and accordingly the noise field intensity caused by the spark discharge will be reduced.

Attempts have also been made wherein the amount of the metal powder in the conductive glass is gradually reduced so as to obtain the conductive glass having a proper resistance value. However, the resistance value of the thus obtained conductive glass largely changes with the minute change of amount of the metal powder, so that it is very difficult to produce the conductive glass having a constant resistance value. Moreover, it is found that the durable life property under load (which is shown by a secular variation rate of the resistance value of the resistor caused by the repetition of the spark discharge) becomes also worse so that this process can not be used practically.

In one embodiment of the invention a spark plug incorporating resistor comprises a ceramic insulator, a metal shell for housing the insulator, an outer electrode connected to the shell and a center electrode opposed to the outer electrode and extended through and sealed in a center bore provided in the insulator, said center electrode being composed of a discharge electrode portion, a terminal electrode portion, a carbonaceous resistor, a conductive glass positioned at one end of the resistor and an auxiliary sealing resistor positioned at the other end of the resistor. The conductive glass, the carbonaceous resistor and the auxiliary resistor are placed between the discharge and the terminal electrode portions. According to the invention the conductive glass can be replaced by the auxiliary resistor, which mainly consists of a glass and a semiconductive material. To the auxiliary resistor may also be added an aggregate, if necessary. The semiconductive material of the auxiliary resistor according to the invention consists of at least one metal oxide such as TiO, Nb O NiO, La O ZrO Th0 and ZnO and at least one metal carbide such as TiC, SiC and B ,C. The aggregate is betonite, clay, zircon or the mixture thereof and the glass is preferably a borosilicate glass.

A preferred composition of the auxiliary resistor according to the invention includes 10-60% of the semiconductive material, up to 30% of the aggregate and 40-90% of the glass.

It is preferable that the carbonaceous resistor has a composition consisting of 0.24% of the carbonaceous material such as carbon black, glycerin or the like, 10-70% of the aggregate such as clay or zircon and the remainder of a barium borate glass and contains less than 20% of a semiconductive material such as a mixture of TiO and TiC, if necessary, so that the resistor shows a resistance value within the range of l-30 K!) which is necessary for effective preventing the noises.

Other objects and aspects of the invention will become apparent from the following description of embodiments with reference to the accompanying drawing, in which:

The drawing is a side elevational view, partly in a cross section of a spark plug in accordance with the invention.

Referring now to the drawing, reference numeral 1 indicates a spark plug ceramic insulator made of porcelain such as high 1 which comprises a small diameter bore 10 for retaining a discharge electrode portion 2 and a large diameterbore 1b for inserting athreaded terminal electrode portion 3, these bores being connected by a tapered shoulder 10. A flange 2a at one end of the electrode portion 2 is retained by the tapered shoulder 10 of the insulator and a discharge end 2b thereof projects from the lower end of the insulator through the small bore 1a. The threaded terminal electrode portion 3 comprises a rod 3a which is placed in the large bore lb of the insulator, a flange 3b which is fixed to the top end of the insulator, a screw portion 3c which is coupled with an external cable (not shown) and a threaded or knurled part 3d for preventing rotation of the terminal electrode portion 3.

Numeral 4 designates a carbonaceous resistor consisting of a glass, an aggregate and a carbonaceous material, the resistor being so located between the flange 2a of the discharge electrode portion 2 and the threaded part 3d of the terminal electrode portion 3 in the large bore 1b of the insulator 1 as not directly to contact them. Numeral 5 shows a conductive glass consisting of a glass and a metal, which is inserted between the carbonaceous resistor 4 and the threaded part 3d of the terminal electrode portion 3. Numeral 6 designates an auxiliary sealing resistor inserted between the carbonaceous resistor 4 and the flange 2a of the discharge electrode portion 2 and mainly consisting of a glass and a semiconductive material (or a glass, a semiconductive material and an aggregate). The auxiliary resistor serves for elongation of the length of an effective resistance part in the insulator bore.

In the present invention, opposed to the above description the auxiliary resistor 6 may be located between'the central resistor 4 and the terminal electrode portion 3, and the conductive glass 5 may in turn be placed between the resistor 4 and the discharge electrode portion 2. Alternatively, the auxiliary resistor in accordance with the invention can be used between the resistor 4 and the terminal and the discharge electrode portions 2, 3 without the conventional conductive glass, and in this case the length of the effective resistance portion can be further elongated.

In the FIGURE, reference numeral 7 shows a metal shell caulked onto the insulator with the aid of an a caulking powder 8 such as talc and a metal packing 9 and numeral 10 designates an outer electrode (usually an earthed electrode) extending from the lower end face of the metal shell and forming a spark gap with the discharge end 2b of the discharge electrode portion therebetween.

In assembling, the discharge electrode 2 made of a Ni alloy is first inserted into the small bore 1a (diameter: 2.8 mm, length: 16 mm) through the large bore 1b of the center bore formed in the insulator and is engaged or retained by the tapered shoulder 1c, and an electrically conductive glass powder in which a lead borosilicate glass powder is mixed with a copper powder in the mixture ratio by weight of 1:] (refer as a first conductive glass hereinafter) is filled onto the flange 2a of the discharge electrode 2 in a height of 3 mm through the large bore 1b (diameter: 4.6 mm, length: 49.5 mm) and then the carbonaceous resistor powder consisting of 30 parts by weight of barium borate glass, 70 parts by weight of a mixture consisting of gairome-clay and zircon in the mixture ratio by weight of 1:1 and 4 parts by weight of glycerin is superimposed thereon in a height of l 1 mm, thereafter the same conductive glass powder as the first conductive glass powder as described above (hereinafter refer as a second conductive glass) is further superimposed thereon in a height of 3 mm. Then, the ceramic insulator thus filled with the conductive glass and the resistor material is heated at 970C for 7 minutes to soften the conductive glass seal powders and the resistor composition and then a pressure of l2 Kg/cm is applied to the terminal electrode 3 to force it down into the center bore, whereby the bottom of the terminal electrode, the upper glass seal, the resistor composition, the lower glass seal and the top of the dis charge electrode are bonded and integrated. The thus formed insulator assembly incorporating a resistor is then assembled in a metal shell 7 having 14 mm of a fitting thread. This process results in manufacture of a conventional glass sealed spark plug A incorporating a resistor.

A spark plug B in accordance with the invention is provided on the same conditions as those of the spark plug A described just above except that an auxiliary resistor powder consisting of 72 parts by weight of borosilicate glass powder, 5 parts by weight of bentonite, 18 parts by weight of TiO and 5 parts by weight of TiC is used instead of the first conductive glass between the resistor 4 and the discharge electrode portion 2. Another spark plug C in accordance with the invention is provided on the same conditions as those of the spark plug A except that the same auxiliary resistor powder as that of the spark plug B is used instead of the second conductive glass between the resistor 4 and the electrode portion 3. A spark plug D in accordance with the invention is provided in the same manner as the spark plug A except that the same auxiliary resistor powders as those of the spark plugs B and C are used instead of the first and the second conductive glasses between the resistor 4 and the discharge and the terminal electrode portions, respectively. Each of the resultant spark plugs A, B, C and D is tested for the durable life property under load, the temperature property and the noise field intensity. The obtained results are shown in the following Table l.

The durable life property under load herein means the variation percentage (within t30%) of the resistance value after 250 hours defined in J IS D5 102-1960, 4, 4, l l and the temperature property means the following value. The resistance value between the discharge and the terminal electrode portions is first determined at room temperature and then the spark plug is subjected to the spark test at 300C for 2 hours and then left to stand for 30 minutes at the room temperature, thereafter, the resistance value is again measured and the variation percentage is determined.

The noise field intensity means a measured value around the frequency of MHZ, obtained by the test defined by Japan Radio Technical Council.

As seen from the above Table l, the spark plug A in which the carbonaceous resistor 4 sandwiched by the conductive glasses is inserted between the discharge electrode portion 2 and the terminal electrode portion 3 oppositely located in the center bore of the insulator,

has a good durable life property under load and a good temperature property but has a large noise field intensity. On the contrary, the spark plugs B, C and D ac cording to the invention in which the auxiliary resistor consisting of glass and semiconductive material is used instead of at least one of the conductive glass between the discharge and the terminal electrode portions so that the length of the effective resistance portion is elongated, have a good durable life property under load and a good temperature property as the spark plug A and have a small noise field intensity with respect to that of the spark plug A. Particularly, the noise fieldintensity of the spark plug D having the longest effective resistance portion shows a minimum value, in the noise tions is maintained during the-use of the spark plug for a long period of time. Therefore, there is no fear that the burning or oxidation of carbonaceous matter occurs at the contacting faces of the resistor to the electrode, and hence the resistance value of the resistor becomes stable.

The aggregate such asbetonite or the like is used to further rise the noise preventing effect by suppressing the fluidity of the auxiliary resistor during the glass sealing operation and by making the joint'(the boundary) of the aggregate with the carbonaceous resistor linear. However, as seen from the samples D D shown in Table 2 the amount of the aggregate added is limited to 30% by weight in the total amount of the field intensity. 15 composition so that upon exceeding this limitation the Then, samples of spark plugs, D D2, 3. D4, 5, D6 fluidity is reduced and then the durable life property and D in accordance with the invention, in which the under l d or h lik becomes worse, compositions Ofthe auxiliary resistors are y changed In the present invention the resistance value of the as Show" Table 2 and the auxlllal'y reslstors are auxiliary resistor mainly consisting of glass and semi-, inserted and sealed between the carbonaceous resistor 20 conductive i l referably e to h same value as and the discharge and the terminal electrode Portions or a certain value lower than that of the carbonaceous (without the conventional conductive glass), are proresistor, i to loo-3,000 Q/ Vided and tested and the performancfi of the thus Moreover, the metal carbide in the auxiliary resistor tamad Spark Plugs are Show" Table according to the invention serves as a kind of reducing Table 2 Semiconductive material Durable Borosilicate Metal oxide, Metal Aggregate life Temper- Noise glass carbide bentonite property ature field (parts by (parts by weight) (parts by (parts by under property inten-- weight) weight) weight) load sity TiO Nb O,-, NiO L320; TiC SiC B4C (7c) (71 (dB) D 75 is I 5 -3-13 37-45 35 D 70 10 5 5 1o +3-10 -3s-45 36 D 70 5 s +8- +2 37-47 35 D, 70 I5 5 5 5 +5-l0 -35-45 35 D 90 2 8 0 +8-ll 35-45 35 D,, 50 10 10 +21-+10 --43 35 D I0 15 35 +35-+25 -35-46 37 Then, the compositions of the carbonaceous resistor 40 agent for the metal oxide during heat sealing and brings 4 in the spark plugs D -D are only changed as shown in Table 3. The test performances of the thus obtained spark plugs D D and D are shown in Table 3.

about the semiconductive property of the metal oxide. As a result of this the auxiliary resistor having a suitable resistance value can be obtained, while the existence of Table 3 Barium Carbonaceous semiconductive Durable life Temper- Noise borate aggregate material material property ature field glass clayzzircon (parts by weight) (parts by weight) under load property intensity (parts by 111 Carbon Glycerin weight) black TiO- Tic (7:) (7r) (dB) D, 30 70 0.3 3 +1 -l0 -33--42 34 D, 30 70 4 l0 +3--l l 38-47 34 D 30 70 3 2 3- 9 38-45 34 The advantageous effect according to the invention as proved by the above examples is generally obtained by elongation of the length of the effective resistance portion in the insulator bore when the present auxiliary sealing resistor is used functionally with the carbonaceous resistor and the electrode portions. Particularly, when the mixture consisting of 40 to 90% by weight of glass, 10 to by weight of semiconductive material and up to 30% by-weight of aggregate, instead of the conductive glass is used as an auxiliary resistor to extend the effective resistance portion and a discharge voltage is applied across the discharge electrode portion and the terminal electrode portion, the low contact resistance between the resistor and the electrode porthe metal oxide serves to prevent the deterioration of the durable life property under load of the auxiliary resistor caused by the existence of the metal carbide after heat sealing. Therefore, the auxiliary resistor exhibits an excellent performance when the metal carbide is contained by 01-30% by weight, preferably 05-10% by weight in the total amount of the auxiliary resistor.

As seen from the above descriptions the resistor incorporating spark plug according to the invention constructed by sealing the carbonaceous resistor with the auxiliary resistor between the discharge and the terminal electrodes opposing each other in the center bore of the ceramic insulator, has sustantially elongated the length of the effective resistance portion, in the insulator bore, so that the noise field intensity produced from the present resistor-incorporated spark plug becomes very small, and thefurther durable life property under load and the temperature property become superior to those of the conventional one and then the effect for preventing noises is certainly maintained during the use of the present resistor-incorporated spark plug for a long period of time.

What is claimed is:

1. In a spark plug comprising a ceramic insulator, a metal shell for housing the insulator, an outer electrode connected to the shell and a center electrode opposed to the outer electrode and extended through and sealed in a center bore provided in the insulator, said center electrode being composed of conductive glasses and a resistor sandwiched by the conductive glasses inserted between a discharge electrode portion and a terminal electrode portion, an improvement comprising using an auxiliary resistor consisting mainly of a glass and a semiconductive material instead of at least one of said conductive glasses, whereby the length of an effective resistance portion of the resistor is elongated.

2. A spark plug as claimed in claim 1, wherein an aggregate is added to the auxiliary resistor.

3. A spark plug as claimed in claim 2, wherein said auxiliary resistor consists of at least one metal oxide and at least one metal carbide as a semiconductor material, an aggregate and a glass.

4. A spark plug as claimed in claim 3, wherein said metal oxide is selected from the group consisting of: TiO Nb O NiO, 1.3 0 ZrO ThO or ZnO.

5.'A spark plug as claimed in claim 3, wherein said metal carbide is selected from the group consisting of: TiC, SiC, or B C.

6. A spark plug as claimed in claim 3, wherein said aggregate is selected from the group consisting of: bentonite, clay or zircon. I I 7. A spark plug as claimed in claim 3, wherein said glass is borosilicate glass.

8. A spark plug as claimed in claim 2, wherein said auxiliary resistor is a composition of 10-60% of the semiconductive material, O.130% of the aggregate and 40-90% of the glass.

9. Aspark plug as claimed in claim 1, wherein said resistor consists of 0.24% carbonaceous material, lO-%.aggregate and the remainder of barium borate glass, and contains less than 20% of semiconductive material.

10. A spark plug as claimed in claim 9, wherein said carbonaceous material is carbon black or glycerin.

' 11. A spark plug as claimed in claim 9, wherein said aggregate is clay or zircon.

12. A spark plug as claimed in claim 9, wherein said semiconductive material is TiO or TiC.

13. A spark plug as claimed in claim 9, wherein the resistance value of the resistor is 1-30 KQ/cm.

14. A spark plug as claimed in claim 3, wherein the resistance value of the auxiliary resistor is -3,000 Q/cm 

1. In a spark plug comprising a ceramic insulator, a metal shell for housing the insulator, an outer electrode connected to the shell and a center electrode opposed to the outer electrode and extended through and sealed in a center bore provided in the insulator, said center electrode being composed of conductive glasses and a resistor sandwiched by the conductive glasses inserted between a discharge electrode portion and a terminal electrode portion, an improvement comprising using an auxiliary resistor consisting mainly of a glass and a semiconductive material instead of at least one of said conductive glasses, whereby the length of an effective resistance portion of the resistor is elongated.
 2. A spark plug as claimed in claim 1, wherein an aggregate is added to the auxiliary resistor.
 3. A spark plug as claimed in claim 2, wherein said auxiliary resistor consists of at least one metal oxide and at least one metal carbide as a semiconductor material, an aggregate and a glass.
 4. A spark plug as claimed in claim 3, wherein said metal oxide is selected from the group consisting of: TiO2, Nb2O5, NiO, La2O3, ZrO2, ThO2 or ZnO.
 5. A spark plug as claimed in claim 3, wherein said metal carbide is selected from thE group consisting of: TiC, SiC, or B4C.
 6. A spark plug as claimed in claim 3, wherein said aggregate is selected from the group consisting of: bentonite, clay or zircon.
 7. A spark plug as claimed in claim 3, wherein said glass is borosilicate glass.
 8. A spark plug as claimed in claim 2, wherein said auxiliary resistor is a composition of 10-60% of the semiconductive material, 0.1-30% of the aggregate and 40-90% of the glass.
 9. A spark plug as claimed in claim 1, wherein said resistor consists of 0.2-4% carbonaceous material, 10-70% aggregate and the remainder of barium borate glass, and contains less than 20% of semiconductive material.
 10. A spark plug as claimed in claim 9, wherein said carbonaceous material is carbon black or glycerin.
 11. A spark plug as claimed in claim 9, wherein said aggregate is clay or zircon.
 12. A spark plug as claimed in claim 9, wherein said semiconductive material is TiO2 or TiC.
 13. A spark plug as claimed in claim 9, wherein the resistance value of the resistor is 1-30 K Omega /cm3.
 14. A spark plug as claimed in claim 3, wherein the resistance value of the auxiliary resistor is 100-3,000 Omega /cm3. 